Analytical Solution for Longitudinal Seismic Responses of Pipelines and Tunnels Crossing Soft‐Hard Rock Strata Based on Double‐Beam Model

ABSTRACT Buried pipelines are susceptible to earthquake‐induced damage when crossing soft‐hard rock strata in high‐intensity seismic regions. In mitigation, pipelines are usually installed within tunnels and buried under backfill materials. The existing seismic calculation method for pipelines does not consider the effects of tunnels. In this study, the pipeline‐tunnel system crossing soft‐hard rock strata is longitudinally simplified to an elastic foundation double‐beam. Green's function is employed to derive the analytical solution for the longitudinal seismic response of the pipeline‐tunnel system, whose validity is verified through numerical models and literature data. A parametric analysis is conducted through the control variable method. As the elastic modulus ratio between the hard and soft rocks increases, the peak internal forces of the pipeline and tunnel near the interface increase significantly. Specifically, the peak bending moments display a double‐peak pattern, while the peak shear forces present a single‐peak one. With the increase in the lining elastic modulus and thickness, the peak internal forces of the pipeline near the interface decrease, while those of the tunnel increase significantly. The peak internal forces of the pipeline increase sharply with the pipeline thickness, whereas those of the tunnel are hardly affected. The shaking table test results demonstrate that the tunnel crossing the interface sustained more severe damage than that in other segments, with oblique shear cracks appearing. This indicates that the sudden increase of the shear forces near the interface is one of the vital reasons for the structural damage, which verifies the rationality of the analytical solution.